Backstepping control called a novel nonlinear strategy is one of the high focus research in ac servo drive for simple arithmetic and facility project implementation.

反推控制是一种新颖的非线性控制策略，算法简单，易于工程实现，是目前交流伺服控制研究热点之一。

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On the other hand, I had an early facility with language, but it was my complete hopelessness with arithmetic that was the single dominant experience of my young life.

NPR: Living With an Inability to Do Math